1. Field of the Invention
This invention relates to a cylinder without a piston rod. In the cylinder without a piston rod, a piston, connected to a tension means, is guided in a cylinder, so that the piston can move in the axial direction. The cross section and/or external circumference of the piston matches the cross section of the cylinder chamber.
2. Background of the Invention
Piston-cylinder aggregates are often used for pneumatic or hydraulic propulsion devices. To reduce the longitudinal dimensions of piston-cylinder aggregates, the prior art omits piston rods and uses flexible tension means to move the piston. The tension means thereby moves a slide, which slide is guided parallel to the axis of movement of the piston. Such drive mechanisms are generally designated cylinders without a piston rod.
Such a cylinder without a piston rod is disclosed in a brochure published by the Knorr Company (No. P 4311-1/2000/0389). In the Knorr Company cylinder without a piston rod, a piston having a round cross section is guided in a correspondingly round cylinder chamber. The piston itself is connected at both ends to the tension means, whereby the tension means is guided outside the cylinder chamber by pulleys installed there, and the tension means is connected to a slide which can move in the axial direction parallel to the axis of movement of the piston. The tension means is fastened eccentrically on the piston, in relation to the longitudinal axis or the center of gravity axis of the piston. Fastening the tension means eccentrically has the disadvantage, however, that during operation the piston experiences a tipping moment in relation to the longitudinal axis of the piston, which leads to uneven wear on the sealing elements. Such a tipping also leads to an uneven sequence of movements of the piston in the cylinder. An additional disadvantage, of these cylinders without a piston rod of the prior art, is the high cost of assembly of the individual elements. This high cost results essentially from the installation and attachment of the tension means.
Laid Open Federal Republic of Germany Patent Application Number DE 29 38 332 A1 discloses an additional work cylinder without a piston rod with tension means, in which the tension means consists of a tension band which is fastened to the piston and which tension band extends beyond the cylinder chamber. The tension band is also deflected outside the cylinder chamber via rollers, so that the linear motion of the piston can be transferred outside the cylinder chamber. For this purpose, certain sizes and dimensions of the cylinder, piston, tension band, and rollers are aimed at achieving a high fatigue strength and high endurance. Such a cylinder without a piston rod also requires a very precise manufacture of the individual parts and a complex assembly process. The cost of this assembly increases with increasing requirements for accuracy and precision of positioning.